Magnetic head having CPP sensor with improved biasing for free magnetic layer

ABSTRACT

A magnetic head for a hard disk drive having a CPP read head sensor that includes a layered sensor stack including a free magnetic layer and hard bias elements that are disposed on the sides of the free magnetic layer to provide a biasing magnetization for the free magnetic layer. To increase the coercivity of the hard bias elements, and thereby improve the biasing of the magnetization of the free magnetic layer, the ratio (t/H) of the thickness t to the height H of the hard bias elements is fabricated to be within the range of from approximately 1 to approximately 1/15.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to read head portions ofmagnetic heads for hard disk drives and more particularly to currentperpendicular to plane (CPP) tunnel junction read sensors for magneticheads.

2. Description of the Prior Art

A computer disk drive stores and retrieves data by positioning amagnetic read/write head over a rotating magnetic data storage disk. Thehead reads from or writes data to concentric data tracks defined onsurface of the disks. The heads are fabricated in structures called“sliders” and the slider flies above the surface of the disk on a thincushion of air, where the surface of the slider which faces the disks iscalled an Air Bearing Surface (ABS).

Some recent read sensor structures use a tunnel junction sensor, alsoknown as a “tunnel valve” for reading the magnetic field signals fromthe rotating magnetic data storage disk. The tunnel junction sensortypically includes a nonmagnetic tunnel barrier layer sandwiched betweena pinned magnetic layer and a free magnetic layer. The pinned layer inturn is fabricated on an antiferromagnetic (AFM) pinning layer whichfixes the magnetic moment of the pinned layer at an angle of 90 degreesto the air bearing surface (ABS). The magnetic moment of the free layeris free to rotate from a quiescent or zero bias point position inresponse to magnetic field signals from magnetic data bits written onthe rotating magnetic disk. Hard bias elements are typically disposed oneither side of the free magnetic layer to provide the necessarymagnetization bias for the free magnetic layer. The tunnel junctionsensor layers are typically disposed between first and second magneticshield layers, where these first and second shield layers also serve asfirst and second electrical lead layers for conducting a sensor currentthrough the device. The tunnel junction sensor is thus configured toconduct sensor current perpendicular to the planes (CPP) of the filmlayers of the sensor, as opposed to previously developed sensors wherethe sensor current is directed in the planes (CIP) or parallel to filmlayers of the sensor. The CPP configuration is attracting more attentionrecently, as it apparently can be made to be more sensitive than the CIPconfiguration, and thus is more useful in higher data density tracks anddisks.

Improved hard disk drives are manufactured with an ever increasing arealdata storage density, which requires narrower and more closely spaceddata tracks on the hard disk. As a result, size of the read sensors mustbe reduced, and as the size of the sensors is reduced the stabilizationof the free magnetic layer by the hard bias elements is becoming aproblem. Additionally, the stabilization of the hard bias elements hasalso become a problem where the sensors are reduced in size.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide increased stabilization ofthe magnetization of the hard bias element, which in turn providesincreased stabilization of the magnetization of the free magnetic layer,which results in improved performance characteristics for the smallerread sensors that are utilized in higher density hard disk drives.

An embodiment of the present invention includes a magnetic head having aCPP read head sensor. The CPP sensor includes a layered sensor stackincluding a free magnetic layer, a tunnel barrier layer, a pinnedmagnetic layer and an antiferromagnetic layer. Hard bias elements aredisposed on the sides of the free magnetic layer to provide a biasingmagnetization for the free magnetic layer.

To increase the coercivity of the hard bias elements, and therebyimprove the biasing of the magnetization of the free magnetic layer, theratio (t/H) of the thickness t to the height H of the hard bias elementsis fabricated to be within the range of from approximately 1 toapproximately 1/15. This is a reduction of the height (H) of the hardbias elements as compared to the prior art. This reduced height H of thehard bias elements increases the shape anisotropy of the hard biaselements, resulting in stiffness of the hard bias elements.

It is an advantage of the magnetic head of an embodiment of the presentinvention that it includes a CPP read sensor having improved biasing ofthe magnetization of the free magnetic layer.

It is another advantage of the magnetic head of an embodiment of thepresent invention that it includes a CPP read sensor having hard biaselements with increased magnetic stiffness.

It is a further advantage of the magnetic head of an embodiment of thepresent invention that it includes a CPP read sensor having hard biaselements wherein shape anisotropy is utilized to increase the magneticstiffness of the hard bias elements.

It is an advantage of a hard disk drive of an embodiment of the presentinvention that it includes the magnetic head of the present inventionhaving a CPP read sensor having hard bias elements with increasedmagnetic stiffness.

It is another advantage of a hard disk drive of an embodiment of thepresent invention that it includes the magnetic head of the presentinvention having a CPP read sensor having improved biasing of themagnetization of the free magnetic layer.

It is a further advantage of the hard disk drive of an embodiment of thepresent invention that it includes a magnetic head of the presentinvention that it includes a CPP read sensor having hard bias elementswherein shape anisotropy is utilized to increase the magnetic stiffnessof the hard bias elements.

These and other features and advantages of embodiments of the presentinvention will no doubt become apparent to those skilled in the art uponreading the following detailed description which makes reference to theseveral figures of the drawing.

IN THE DRAWINGS

The following drawings are not made to scale as an actual device, andare provided for illustration of the invention described herein.

FIG. 1 is a top plan view depicting a hard disk drive of an embodimentof the present invention having a magnetic head of an embodiment of thepresent invention;

FIG. 2 is a side cross-sectional view of a tunnel barrier sensor portion30 of a prior art magnetic head 32 taken along lines 2-2 of FIGS. 3 and4;

FIG. 3 is a side elevational view of the tunnel barrier sensor 30depicted in FIG. 2, taken from the air bearing surface of the magnetichead 32 along lines 3-3 of FIG. 2;

FIG. 4 is a top plan view depicting the tunnel barrier sensor portion 30of the prior art magnetic head 32 taken along lines 4-4 of FIG. 3;

FIG. 5 is a side elevational view of the tunnel barrier sensor of amagnetic head of an embodiment of the present invention taken from theair bearing surface of the magnetic head; and

FIG. 6 is a top plan view depicting the tunnel barrier sensor portion ofthe magnetic head of an embodiment of the present invention taken alonglines 6-6 of FIG. 5.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a top plan view that depicts significant components of a harddisk drive 10 of the present invention which includes the magnetic headof an embodiment of the present invention. The hard disk drive 10includes a magnetic hard disk 12 that is rotatably mounted upon amotorized spindle 14. An actuator arm 16 is pivotally mounted within thehard disk drive 10 with a slider device 20 having a magnetic head 100 ofan embodiment of the present invention disposed upon a distal end 22 ofthe actuator arm 16. A typical hard disk drive 10 may include aplurality of disks 12 that are rotatably mounted upon the spindle 14 anda plurality of actuator arms 16 having a plurality of sliders 20 mountedupon the distal ends 22 of the plurality of the actuator arms 16. As iswell known to those skilled in the art, when a hard disk drive isoperated, the hard disk 12 rotates upon the spindle 14 and the slideracts as an air bearing that is adapted for flying above the surface ofthe rotating disk. The slider includes a substrate base upon whichvarious layers and structures that form the magnetic head 100 arefabricated. Such sliders with their magnetic heads are typicallyfabricated in large quantities upon a wafer substrate and subsequentlysliced into discrete devices.

A typical magnetic head will include both a read head portion and awrite head portion. The read head portion is utilized to read data thathas been written upon the hard disk 12, and the write head portion isutilized to write data to the disk 12. Read head sensors are generallyof two types, current-in-plane (CIP) and current-perpendicular-to-plane(CPP) as is well known to those skilled in the art. Embodiments of thepresent invention are directed to the read head portion of a magnetichead, and particularly to such read heads that include a CPP sensor,which includes sensors that may have a tunnel barrier structure, as isnext described with aid of FIGS. 2, 3 and 4.

FIG. 2 is a side cross-sectional view of a tunnel barrier sensor portion30 of a prior art magnetic head 32 taken along lines 2-2 of FIGS. 3 and4, FIG. 3 is a side elevational view of the tunnel barrier sensor 30depicted in FIG. 2, taken from the air bearing surface of the magnetichead 32 along lines 3-3 of FIG. 2, and FIG. 4 is a top plan viewdepicting the tunnel barrier sensor portion 30 of the prior art magnetichead 32 taken along lines 4-4 of FIG. 3. As is best seen in FIGS. 2 and3, the tunnel barrier sensor 30 includes a plurality of thin filmlayers. These layers include a first magnetic shield layer 34 that isfabricated upon or over an electrical insulation layer 36 that isdeposited upon a wafer substrate 38. While many different layered sensorstructures are known in the prior art, a typical sensor layer structurewill include an antiferromagnetic layer 42 which may be comprised of aPt—Mn or Ir—Mn alloy that is fabricated upon or over the first magneticshield layer 34. A pinned magnetic layer 46 is fabricated upon or overthe antiferromagnetic layer 42, and it may be comprised of a magneticmaterial such as a Co—Fe alloy. The direction of magnetization of thepinned magnetic layer (see arrow 48) is generally perpendicular to theair bearing surface (ABS) of the magnetic head.

Thereafter, a tunnel barrier layer 50 is fabricated upon or over thepinned magnetic layer 46, where the tunnel barrier layer 50 may becomprised of an electrical insulation material such as MgO_(x), TiO_(x)and AlO_(x) where the subscript x indicates that the oxide need not bestoichiometric. In alternative CPP sensor embodiments, the CPP sensormay be of the GMR type, wherein the layer above the pinned magneticlayer is electrically conductive, such as copper. However, for purposesof description, a CPP sensor with a tunnel barrier layer will bedescribed herein, it being understood that the novel features of thepresent invention are equally applicable to such CPP GMR sensors.

A free magnetic layer 54 is then fabricated upon or over the tunnelbarrier layer 50, where the free magnetic layer 54 may be composed of amagnetic material such as a Co—Fe alloy or a Ni—Fe alloy. The directionof magnetization of the free magnetic layer (see arrow 56) is nominallyin the plane of the free magnetic layer, however it is free to rotate inresponse to the magnetic field of magnetic data bits of the disk 12.Thereafter, a cap layer 62 is typically fabricated upon or over the freemagnetic layer 54, and a typical cap layer may be comprised of amaterial such as tantalum and/or ruthenium. As can be best understoodwith the aid of FIGS. 3 and 4, the layers 42-62 are then masked and ionmilled in a plurality of steps to create a central sensor stack 64having a back wall 66 and side walls 70. As seen in the top plan view ofFIG. 4, the distance W between the side walls 70 of the sensor 30defines the read width of the sensor.

Following the ion milling steps for creating the back wall 66 and sidewalls 70, a thin layer of electrical insulation 74 is next depositedupon or over the device, particularly upon the side walls 70, utilizinga process such as atomic layer deposition (ALD). Thereafter, magnetichard bias elements 76, typically composed of a material such as a Co—Ptalloy, are fabricated upon the insulation layer 74 proximate the sidewalls 70. The back edge 80 of the hard bias elements 76 extendssignificantly beyond the back wall 66 of the sensor stack. The directionof magnetization of the hard bias elements (see arrows 82) is desirablyin the same direction as the magnetization 56 of the free magneticlayer, in that the magnetization of the hard bias element stabilizes thefree magnetic layer 54. A second magnetic shield 86 is then fabricatedupon the cap layer 62 and hard bias elements 76. In fabricating the head32, following the fabrication of the read head structures, and followingsubsequent fabrication steps to create write head structures (notshown), an air bearing surface (ABS) 94 is created. The distance betweenthe ABS 94 and the back wall 66 of the sensor stack is termed the stripeheight (SH) of the sensor, and in this application the distance betweenthe ABS and the back edge 80 of the hard bias elements will be termedthe height (H) of the hard bias elements.

A magnetic head including a tunnel barrier sensor 30 operates by thepassage of electrical sensor current from the first magnetic shield 34,through the sensor layers 42-62 and into the second magnetic shield 86,such that the current travels perpendicular to the planes (CPP) of thelayers 42-62. The electrical insulation layer 74 serves to guide thesensor current through the sensor layers. The tunnel barrier sensor,such as is depicted in FIGS. 2-4 operates by detecting magnetic databits written upon the hard disk 12 through a change in electricalresistance within the sensor when the sensor is exposed to the magneticfield of the data bit. Specifically, the direction 56 of the free layermagnetization is altered by the magnetic field of a data bit, and thechange in the direction of the free layer magnetization creates a changein the electrical resistance of the sensor. This change in theresistance then affects the electrical current flowing through thesensor, and the change in sensor current flow is detected andinterpreted as a data signal. The biasing magnetic field 82 from thehard bias elements serves to urge the direction of magnetization 56 ofthe free magnetic layer to its nominal direction shown in FIGS. 2-4. Theoperational characteristics of tunnel barrier sensors are well known tothose skilled in the art, and a more detailed description thereof is notdeemed necessary in order to fully describe the features of the presentinvention.

Improved hard disk drives are manufactured with an ever increasing arealdata storage density, which requires narrower and more closely spaceddata tracks on the hard disk and a higher bits per inch (BPI) in thedata tracks. As a result, the size of the MR sensors must be reduced,and as the size of the MR sensors is reduced the stabilization of thefree magnetic layer by the hard bias elements is becoming a problem.Additionally, the stabilization of the hard bias elements also becomes aproblem when the magnetic heads are reduced in size. Particularly, as isdepicted in FIG. 4, where the hard bias elements are reduced in size,the direction of magnetization 82 can rotate (see arrow 96) in responseto external magnetic fields or other events that the magnetic head mayencounter. Where the direction of magnetization of the hard biaselements is altered (such as arrow 98) the biasing of the free magneticlayer 54 is detrimentally affected, and the performance of the CPPsensor may be significantly diminished. As indicated herebelow, thepresent invention provides improved stabilization of the magneticproperties of the hard bias elements, thereby providing improvedstabilization to the free magnetic layer. As will be seen, the improvedstabilization of the hard bias elements is achieved through improvedshape anisotropy which enhances the coercivity and stiffness of the hardbias magnetization, as is next described.

The improved magnetic head 100 of the present invention, including animproved CPP sensor 110, is depicted in FIGS. 5 and 6, in which FIG. 5is an elevational view taken from the air bearing surface of themagnetic head 100, and FIG. 6 is a plan view taken from lines 6-6 ofFIG. 5. As will be understood when reading the following description,the significant difference between the magnetic head 100 of the presentinvention and the prior art magnetic head 32 is the shape of the hardbias elements 120 that are fabricated on either side of the CPP sensorstack 64. Therefore, the magnetic head 100 of the present inventionincludes many features and structures that are substantially similar tothose of the prior art magnetic head 32, and such similar structureshave been identically numbered for ease of comprehension.

As can be seen in FIG. 5, the CPP sensor 110 includes a plurality ofthin film layers. These layers include a first magnetic shield layer 34that is fabricated upon an electrical insulation layer 36 that isdeposited upon a wafer substrate 38. While many different layered sensorstructures are known in the prior art, a typical sensor layer structurewill include an antiferromagnetic layer 42 which may be comprised of aPt—Mn or Ir—Mn alloy that is fabricated upon the first magnetic shieldlayer 34. A pinned magnetic layer 46 is fabricated upon theantiferromagnetic layer 42, and it may be comprised of a magneticmaterial such as a Co—Fe alloy. The direction of magnetization of thepinned magnetic layer (see arrow 48) is generally perpendicular to theair bearing surface (ABS) of the magnetic head. Thereafter, a tunnelbarrier layer 50 is fabricated upon the pinned magnetic layer 46, wherethe tunnel barrier layer 50 may be comprised of an electrical insulationmaterial such as MgO_(x), TiO_(x) and AlO_(x) where the subscript xindicates that the oxide need not be stoichiometric. In alternative CPPsensor embodiments of the present invention, the CPP sensor may be ofthe GMR type, wherein the layer above the pinned magnetic layer iselectrically conductive, such as copper. However, for purposes ofdescription, a CPP sensor with a tunnel barrier layer will be describedherein, it being understood that the novel features of the presentinvention are equally applicable to such CPP GMR sensors.

A free magnetic layer 54 is then fabricated upon the tunnel barrierlayer 50, where the free magnetic layer 54 may be composed of a magneticmaterial such as a Co—Fe alloy or a Ni—Fe alloy. The direction ofmagnetization of the free magnetic layer (see arrow 56) is nominally inthe plane of the free magnetic layer, however it is free to rotate inresponse to the magnetic field of magnetic data bits of the disk 12.Thereafter, a cap layer 62 is typically fabricated upon the freemagnetic layer 54, and a typical cap layer may be comprised of amaterial such as tantalum and/or ruthenium. The layers 42-62 are thenmasked and ion milled in a plurality of steps to create a central sensorstack 64 having a back wall 66 and side walls 70. The distance W betweenthe side walls 70 of the sensor 110 defines the read width of thesensor.

A thin layer of electrical insulation 74 is next deposited upon thedevice, particularly upon the side walls 70, utilizing a process such asatomic layer deposition (ALD). Thereafter, magnetic hard bias elements120, typically composed of a material such as a Co—Pt alloy, arefabricated upon the insulation layer 74 proximate the side walls 70. Theheight H of the hard bias elements is reduced as compared to the priorart, and it is shown by way of example in FIG. 6 where the back wall 124is approximately in the same location as the back wall 66 of the sensorstack 64, such that the height H of the hard bias elements 120 isapproximately equal to the stripe height (SH) of the sensor stack. Asecond magnetic shield 86 is subsequently fabricated upon the cap layer62 and hard bias elements 120. Following the fabrication of the readhead structures, and following subsequent fabrication steps to createwrite head structures (not shown), an air bearing surface (ABS) 94 iscreated. The distance between the ABS 94 and the back wall 66 of thesensor stack is the stripe height (SH) of the sensor, and the distancebetween the ABS 94 and the back wall 124 of the hard bias elements 120is the height (H) of the hard bias elements.

The significant features of the present invention are best understood bycomparing the depiction of the present invention in FIG. 6 with thedepiction of the prior art magnetic head shown in FIG. 4. As can be seenin FIG. 6, the height of the hard bias elements 120 is substantiallyreduced from the height of the hard bias elements 76 as is known in theprior art. Specifically, as can be seen in FIG. 6, the preferred heightH of the hard bias elements 120 may be, though not necessarily,approximately the same as the stripe height SH of the sensor stack.

The stabilization of the magnetization of the hard bias elements iscontrolled by the coercivity of the hard bias magnetic material. Thepresent invention utilizes the shape anisotropy to enhance the hard biascoercivity and stiffness. This can be important for hard bias elementmaterials which have excellent squareness but somewhat lower coercivityof approximately 800 to 1200 Oe. Even current hard bias materials with1400 to 1800 Oe coercivity can generally benefit from the shapeanisotropy improvement of the present invention. Assuming a 30 nm thick(t) hard bias element with a 60 to 90 nm height H and approximately 1 umlength, the shape anisotropy related coercivity of the hard bias elementcan be as much as 5000 Oe as is shown below. The shape relatedcoercivity Hk of a hard bias element can be stated as:H _(k)=4πMst/H.Where 4πMs is approximately 10000, and t=30 nm, it can be seen that;

H_(k)=5000 Oe. for H=60 nm; and

H_(k)=3300 Oe. for H=90 nm.

Thus, even for a 90 nm hard bias height H, the shape anisotropy relatedcoercivity is around 3000 Oe which is about twice as much as thecoercivity of the hard bias magnet material itself. This invention thusimproves the coercivity of the hard bias elements by altering the shapeanisotropy of the hard bias elements, and makes the hard bias element'smagnetization stable against any large disturbing magnetic fields.

In a preferred embodiment of the present invention, where the thicknesst can be from approximately 5 nm to approximately 60 nm, thethickness/height ratio (t/H) of the hard bias elements is preferablywithin the range of from approximately 1 to approximately 1/15, with apreferred range of approximately ½ to approximately 1/10. As compared tothe stripe height SH of the sensor stack, where SH can be fromapproximately 10 nm to approximately 100 nm, the height H of the hardbias elements is preferably within the range of from approximately equalto the stripe height SH to approximately three times the stripe heightSH. Hard bias elements that are fabricated within these ranges willgenerally have increased coercivity due to shape anisotropy thatprovides an increased biasing of the free magnetic layer magnetization.As magnetic heads are reduced in size for use in hard disk drives havingincreased areal data storage density, the improved biasing of themagnetization of the free magnetic layer creates improved performancecharacteristics of magnetic heads of the present invention.

The fabrication of the improved hard bias elements can be accomplishedin many different ways, as will be understood by those skilled in theart. One such method is to fabricate the magnetic head utilizing theidentical fabrication steps that are known in the prior art to thefabrication stage in which the hard bias elements 76 are fabricated withthe large height as depicted in FIG. 4. Thereafter, in a new processstep, a milling mask is fabricated to cover the sensor and the desirableportions of the hard bias elements. Thereafter, in an ion milling step,the undesirable extended portions of the hard bias elements are removed.Thereafter, an insulative fill material 132 is deposited and the millingmask is removed. Alternatively, the magnetic head 100 of the presentinvention can be fabricated in a method wherein a first milling step isconducted in which the sidewalls of the central stack are created. Thisis followed by the deposition of the insulation layer 74, followed bythe deposition of the extended hard bias elements (such as 76 in FIG.4). Thereafter, the stripe height SH of the sensor and the height H ofthe hard bias elements 110 are simultaneously created utilizing amilling mask that covers the desired portions of the sensor stack andthe hard bias elements. An ion milling step is then conducted to removeunmasked portions of the hard bias elements 110 and the sensor stack,such that the stripe height SH of the sensor stack and the height H ofthe hard bias element are simultaneously created in this milling step.Fill material 132 is thereafter deposited.

While the present invention has been shown and described with regard tocertain preferred embodiments, it is to be understood that modificationsin form and detail will no doubt be developed by those skilled in theart upon reviewing this disclosure. It is therefore intended that thefollowing claims cover all such alterations and modifications thatnevertheless include the true spirit and scope of the inventive featuresof the present invention.

1. A magnetic head, comprising: a CPP read sensor including a pluralityof sensor layers, wherein said sensor layers are formed with an airbearing surface (ABS), side edges and a back edge that defines a sensorstripe height SH between the ABS and said back edge; hard bias elementsbeing disposed proximate said side edges, said hard bias elements havinga height H and a thickness t, wherein the ratio of t/H is fromapproximately 1 to approximately 1/15; an insulating layer extendingaround a corner of each of the hard bias elements and along a bottom andside of the hard bias element closest the side edges and defining thecorner; and a magnetic shield formed directly on the hard bias elements.2. A magnetic head as described in claim 1 wherein t is within the rangeof from approximately 5 nm to approximately 60 mm.
 3. A magnetic head asdescribed in claim 1 wherein H is within the range of approximately SHto approximately 3 SH.
 4. A magnetic head as described in claim 3,wherein SH is within the range of from approximately 10 nm toapproximately 100 mm.
 5. A magnetic head as described in claim 1 whereinH is within the range of from approximately 20 nm to approximately 300nm.
 6. A hard disk drive, comprising: a rotatable hard disk; a magnetichead as recited in claim 1, said magnetic head being disposed forreading data from said hard disk.
 7. A hard disk drive, comprising: arotatable hard disk; a magnetic head being disposed for reading datafrom said hard disk, said magnetic head, including: a CPP read sensorincluding a plurality of sensor layers, wherein said sensor layers areformed with an air bearing surface (ABS), side edges and a back edgethat defines a sensor stripe height SH between the ABS and said backedge; hard bias elements being disposed proximate said side edges, saidhard bias elements having a height H and a thickness t, wherein theratio of t/H is from approximately 1 to approximately 1/15; aninsulating layer extending around a corner of each of the hard biaselements and along a bottom and side of the hard bias element closestthe side edges and defining the corner; and a magnetic shield formeddirectly on the hard bias elements.
 8. A hard disk drive as described inclaim 7 wherein t is within the range of from approximately 5 nm toapproximately 60 nm.
 9. A hard disk drive as described in claim 7wherein H is within the range of approximately SH to approximately 3 SH.10. A hard disk drive as described in claim 9, wherein SH is within therange of from approximately 10 nm to approximately 100 nm.
 11. A harddisk drive as described in claim 7 wherein H is within the range of fromapproximately 20 nm to approximately 300 nm.